One locking device is described in U.S. Pat. No. 3,376,984 by Long and assigned to the assignee of the present invention. The disclosure of Long relates to what is referred to as an "over-center" boom, that is a boom which can be swung to a transport or storage position that is generally vertical and slightly toward the vehicle side of the boom support. In the Long patent, the boom is held in the transport position by the fluid rams that are used to pivot the boom about a horizontal axis on the boom support. The boom may be swung about a vertical axis by one or more hydraulic rams joining the boom support to the base. Similarly, the boom support may be restrained from swinging freely about its vertical axis during transportation or storage by forming a hydraulic lock in the fluid rams joining the boom support to the base.
Positive interlocks between the boom and the boom support are also disclosed in U.S. Pat. No. 3,811,582 by Shumaker and U.S. Pat. No. 3,921,835 by Baker both assigned to the assignee of the present invention. These latter disclosures do not provide for locking the boom support and thus do not completely lock the boom against rotation in two directions.